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RE: A Mercedes and a bus...

Correct, and I have never disagreed with this-- as far as it goes.....

That same microphone's two balanced output leads would normally be encased in a cable that has a shield around it.

That shield would be grounded-- in some cases, one of the two "hot" leads would also be grounded.

True balanced would have the two leads "hot". S.E. would ground one of the two "hot" leads to the shield in most cases..

In the case of balanced, with a shield NOT connected to either lead, Common-Mode rejection takes place between the two "hot" wires, and to the grounded shield.

In the S.E. example, where one lead is also grounded to the shield, there is no longer a Common-Mode. There's only one "hot" wire. The loss here is "hot lead" energy being absorbed into the shield, and into the grounded lead.

The energy loss in the two balanced "hot" leads with a shield example-- is to load the Common-Mode that is between the two "hot" wires-- into the shield. The Common-Mode is thus attenuated into the shield.

You have losses either way-- into the shield, etc. In the S.E. example, loss is broadband, but not totally-- that depends on what the wire's characteristics are.. In the balanced example, loss is both into broadband and into attenuating the Common-Mode between the two "hot" wires in the shielded cable/interconnect.

Some users prefer to wire the mike as S.E.-- that is, with one "hot" pin grounded with the shield also as ground. For short runs, this sounds more real.

Others don't have time for that and wire everything balanced. For longer runs, and for frequently moved/disturbed studios, this is the way to go.

You are, however, attenuating the Common-Mode mostly because your wire has a shield around BOTH "hot" leads..

What if it didn't have a shield? Just two wires-- balanced. If they're near each other, or twisted together, then the internally radiated Common Mode is also being attenuated by the cable-- even without a shield because the two "hot" leads are close enough to radiate into each other.

There. You have it.

---Dennis---



Edits: 03/14/15
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